1. Field of the Invention
This invention generally relates to digital wrapper format communications and, more particularly, to a system and method for transporting backwards information between simplex devices in a network using a digital wrapper format.
2. Description of the Related Art
Digitally wrapped, or multidimensional frame structure communications generally describe information that is sent as a packet without overhead to control the communication process. The packet can also include forward error correction (FEC) to recover the payload if the communication is degraded. One example of such communication is the synchronous optical network (SONET). Another example is the digital wrapper format often used in transporting SONET communications.
There are many framed communication protocols in use, depending on the service provider and the equipment being used. These differences in protocols can be arbitrary or supported by an underlying function. Frame synchronization and overhead placement are sometimes standardized by governing organizations such as the ITU-T. At the time of this writing, the ITU-T standard for the digital wrapper format is G.709.
Conventionally, the interface node must include two sets of equipment. A communication in the first protocol is received at the first set of equipment (processor). The message is unwrapped and the payload recovered. Synchronization protocols must be established between the equipment set and a second set of equipment (processor). The payload can then be received at the second equipment set and repackaged for transmission in a different protocol.
Systems that are built to be compliant to G.709 must communicate certain error fields upstream in the network. These error fields are transmitted in the allotted backward fields in the overhead part of the data stream. These backward fields are processed by the receiving nodes to determine the health of the downstream transmission link. As of this writing, the backward error fields defined in G.709 that can be used with this invention are the Backward Error Indication (BEI), the Backward Defect Indication (BDI), and the backward field of the Fault Type and Fault Location (FTFL) message. However, other backward fields could be added to the G.709 standard.
FIG. 1 is a schematic block diagram of a full-duplex processing node (prior art). When a G.709 compliant full-duplex processing node is built up from a single integrated circuit device, all the communication of the backward information takes place within that integrated circuit. In this type of device, the injection of the backward errors from one direction of the network to the other can be accomplished without any user intervention.
However, G.709 compliant full-duplex processing nodes can also be built up from two simplex integrated circuit devices, in which case it is no longer possible to communicate the backwards information within a single integrated circuit. This is a problem that must be solved with interface circuitry that is complex, costly, and cumbersome.
It would be advantageous if the backward information received in the dropped overhead data stream by a first simplex device could be replaced with the calculated backward error to be sent upstream by a second simplex device.
It would be advantageous if the above-mentioned simplex devices could be simply interfaced. It would also be advantageous if the calculated backwards errors could be sent in real-time.